1. Field of the Invention
The invention relates to a circuit arrangement for automatically recognizing the line number of a video sync signal in accordance with the 525 or 625 line standard, and for automatically generating a control signal corresponding to one of the relevant line numbers, a sync pulse signal of the horizontal frequency being derived from a main sync pulse generator via a phase-locked loop with a programmable divider arranged in the feedback path of the phase-locked loop.
2. Description Of The Related Art
The currently conventional color television systems make worldwide use of mainly two different line standards, namely, 525 lines at 30 (or 29.97) Hz frame frequency and 625 lines at 25 Hz frame frequency. Post-production television studios generally use the same television equipment, such as telecine scanners, video recorders, color correction apparatus, video mixers, etc., in the different color television standards, i.e., both 525 and 625 lines. To prevent that all television apparatuses connected to the main sync pulse generator of the television studio must be individually switched over when changing the line number, it is desirable to change only the line number when the sync pulses are generated, thus to switch the main sync pulse generator so that all television apparatuses synchronized therewith are simultaneously and automatically adapted to the new line number. To avoid picture drop-outs, a high degree of freedom from interference is required.
A circuit for automatically recognizing different line standards (525/625 lines) is known from U.S. Pat. No. 4,402,011, which circuit is, however, particularly intended for television receivers for domestic use. In this case, only a simple horizontal frequency oscillator having a fixed setting is provided as a sync generator for a line counter.